Glass fibers have long been noted for their insulating value. However, depending upon the end use of the insulation, there are certain disadvantages to be found in glass fiber insulation now in general use. It is well known that in fibrous insulation the respective fibers are bonded to one another by a suitable binder system which normally consists of a phenolic liquid resole resin or a conventional phenolic-formaldehyde resin in combination with various additives. The additives are used to improve either the process characteristics of the binder system or to improve the finished fiberglass product characteristics.
Processes for making mineral fiber thermal insulation are typically carried out according to one of a number of methods wherein the molten mineral material flowing from a melting furnace is divided into streams and attenuated into fibers. The attenuation is done by centrifuging and/or fluid jets to form discontinuous fibers of relatively small dimensions which are collected by randomly depositing on a moving foraminous conveyor belt. The fibers are collected in a felted haphazard manner to form a mat. The volume of fiber in the mat will be determined by the speed of fiber formation and the speed of the belt. In order to produce most thermal insulating products, the fibers must be bonded together in an integral structure. To achieve this binding, a curable binder material is added to the mineral wool. The curable binder composition is generally formulated as a liquid to be sprayed onto the fibers as they are dropping onto the collecting conveyor belt. The layer of fiber with binder is then compressed and shaped into the form and dimensions of the desired thermal insulating product and passed through a curing oven where the binder is cured fixing the size and shape of the finished insulating product. Various materials have been used as binder ingredients including both organic and inorganic materials generally blended for different properties. The organic binder material most commonly employed are heat curable thermosetting resin systems of the phenol-formaldehyde type.
Such binders are generally provided as water soluble or water dispersable compositions which can be easily blended with other ingredients and diluted to low concentrations which are readily sprayed onto the fiber as it falls onto the collecting conveyor. The binder composition is generally applied in an amount such that the cured binder constitutes about 5% to about 10% by wt. of the finished product though it can be as little as 1% or less or as high as 20% or more, depending upon the type of fiber product. Optimally, the amount of binder for most thermal insulating products will be the amount necessary to lock each fiber into the mass by bonding the fibers where they cross or overlap. For this reason, it is desired to have binder compositions with good flow characteristics so that the binder solution can be applied to the fiber at a low volume that will flow to the fiber intersections.
Generally, the binder system requirements are for a low cost water soluble or water dispersable composition which can be easily applied and readily cured during normal production cycles. The product should be relatively stable for periods of time long enough to permit mixing and application at temperatures ordinarily encountered in fiberizing plants and the composition should be dilutable in order to permit variations in concentrations for different end products. The cured binder product must provide a strong bond with sufficient elasticity and thickness recovery to permit reasonable shipping and in-service deformation of the thermal insulating product. It must be moisture resistant so that it will not swell under humid conditions. It must be odor free and non-corrosive to metals with which it comes in contact. The binder should be capable of withstanding temperatures as high as the temperature that the mineral fiber can withstand, particularly for pipe insulation where the pipeline is used for hot fluids. The mineral fibers can be any of the materials which are capable of being fiberized. Typical binder compositions for glass are prepared as aqueous solutions or dispersions of partially condensed phenolic formaldehyde resins to which are added a variety of modifiers or agents to improve the spraying, flowing or similar application characteristics as well as the bonding strength, temperature resistance and other in-service features of the cured resin.